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3. PathWaYS of iNtroduCtioN

3.5. synthesis and indicator values

This chapter has highlighted that south africa has a number of prominent pathways of introduction, and that alien taxa have entered the country through a wide variety of these pathways. once introduced, these organisms are likely to disperse or spread widely. some of the pathways that involve the intentional import of alien taxa are playing an important and increasing role in south africa, and most taxa have been introduced intentionally through these pathways. a large number of alien taxa have been accidentally introduced to south africa. The import of goods such as live plants and food has increased over time and although control measures are in place to prevent the accidental introduction of commodity contaminants, the rate at which alien taxa are being introduced through these pathways has not declined. in south africa, the accidental introduction of alien taxa as stowaways on transport vessels is also playing an important role that is likely to increase in the future;

unfortunately, control measures are not in place for many of these pathways. The natural dispersal of alien taxa into south africa from our neighbouring countries will likely increase in the future, but preventing these introductions will be extremely difficult and to do so would require regional co-operation. overall, the rate of introduction has increased over time and it appears that alien taxa will continue to be introduced at an increasing rate through a wide variety of pathways. once introduced, these taxa can be dispersed with the aid of south africa’s extensive transport networks and can become widespread. further research and better data are required to identify and prioritise these pathways and to develop and evaluate control measures.

ChaPter 3IPaThWaYs of inTroduc

estimation of introduction pathway prominence: socio-economic data for the pathways of introduction were used by an expert to classify the size of the pathways into five categories of introduction pathway prominence. for 12 pathways (27.3%), introduction pathway prominence was not known as socio-economic data for these pathways could not be obtained. one pathway (2.3%) is no longer present due to changes in socio-economic factors. seven pathways (15.9%) play a minor role in south africa, but 12 (27.3%) have a moderate role, and a further 12 (27.3%) play a major role. however, as the data were evaluated by one expert, confidence in this assessment is medium.

estimation of introduction rates and effectiveness of control measures: pathway and date of introduction data for alien species introduced to south africa were used to estimate Introduction rates. as alien taxa can be introduced through more than one pathway, the number of taxa across the pathways might be greater than the number investigated. in some instances, pathway descriptions were vague and it was difficult to make definite categorisations. furthermore, the similarity of some of the pathway subcategories (e.g. ‘contaminant nursery material’ and ‘contaminant on plants’) caused uncertainty. To account for this, certainty in the pathway assignments for each taxon was rated. in instances where pathway of introduction information was not available, or where insufficient information was provided, the pathway was classified as

‘unknown’. in some instances, there was insufficient information to assign pathways at the subcategory level (e.g. the pathway of introduction for many alien bird taxa was described as ‘escape’, with no further details provided). in these instances, a pathway category was assigned and the pathway subcategory was classified as ‘not enough detail provided’.

excluded from the analyses were hybrid taxa, dubious records (e.g. the mollusc Vertigo antivertigo which has only been found as a subfossil (herbert, 2010)), taxa that have not yet escaped from confinement, and those whose regions of origin extend into south africa. Taxa with an uncertain region of origin were excluded unless currently believed to be alien to south africa. Taxa which were listed as alien but for which no information on region of origin was provided were assumed to be alien and were included in the analyses.

The total number of taxa introduced through each pathway was calculated and used to estimate Introduction rates. relatively few taxa have been introduced through most pathways, with only two pathways facilitating the introduction of over 100 taxa. for each pathway, the number of new taxa introduced during each decade from 1950 to 2020 was calculated. by comparing the rate of introduction in the last full decade (2000-2009) to that of the previous decade (1990-1999), recent changes to the rate of introduction were determined. There have been no introductions through 18 of the pathways (40.9%) since 2000. although there have been no introductions through 14 of the pathways (31.8%) since 2000, as taxa have previously been introduced through these pathways and as the data appears to be insufficient, recent changes to the rate of introduction through these pathways were not known. While for one pathway (2.3%) the rate of introduction decreased by five or more taxa, for nine pathways (20.5%) there was minimal change to the rate of introduction (no change or a change of less than 5 taxa), and for 2 pathways (4.5%) the rate of introduction increased by five or more taxa. as pathway and date of introduction data are not available for many taxa, confidence in this assessment is low.

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estimates of recent changes to Introduction rates were used to evaluate the effectiveness of pathway-related control measures, which began to come into effect in the 1980s (e.g. agricultural Pests act (act no. 36 of 1983);

conservation of agricultural resources act (act no. 43 of 1983); animal diseases act (act no. 35 of 1984)). details on the calculations of these estimates are provided in chapter 6.

estimation of within-country pathway prominence: as socio-economic data related to the pathways of dispersal could only be obtained for a few pathways, Within-country pathway prominence was not assessed.

estimation of within-country dispersal rates: as data on Within-country dispersal rates has not yet been collated and only a few examples were obtained, Within-country dispersal rates was not assessed.

estimation of high level indicator – rate of introduction of new unregulated species: the data used to determine the rates of introduction were used to calculate the number of new taxa introduced to south africa each year during the last full decade (2000-2009). The average rate of introduction for the decade was then calculated. 70 new taxa were introduced between 2000 and 2009, with an average introduction rate of 7 taxa per year. as pathway and date of introduction data are not available for many taxa and as it is likely that there is a substantial delay between introduction and detections, confidence in this assessment is low.

forecasts of changes to the pathways of introduction: although future changes to introduction pathways are not directly addressed in the indicators, socio-economic data were used to make forecasts of how introduction pathway prominence might change in the future. socio-economic forecast data were not available for 28 pathways (63.6%) and so future changes to the size of these pathways is not known. however in the future, twelve pathways (27.3%) are expected to increase in size, while there will be minimal change to the size of three pathways (6.8%). future changes to the size of one pathway (2.3%) are very uncertain and there could be an increase or decrease in the size of this pathway.

tABle 3.2 values for the indicators for reporting on the status of the introduction and dispersal pathways, the level of confidence in each assessment and notes on the assigned confidence levels.

indiCAtor vAlue

BASiC AdvAnCed level oF

ConFidenCe noteS

1. introduction pathway prominence


not known:

12 pathways Pathway not present:

1 pathway minor:

7 pathways moderate:

12 pathways major:

12 pathways

1.2. data not available

1.3. data not available

1.1. medium evaluation by one expert

ChaPter 3IPaThWaYs of inTroduc

available 3.2. data not

available 3.3. data not

available n/a data were only collected for a few pathways

4. within-country

dispersal rates 4.1. data not

available 4.2. data not

available 4.3. data not

available n/a Pathway and date of dispersal data for many alien taxa in south africa


live plants and their products are imported into South Africa for a number of uses. for example, as South African consumers in the ornamental plant sector show a desire for new varieties of plants, plants are often imported for this purpose (middleton, 2015). live plant imports to South Africa have increased over time and in 2016 these imports were valued at over 12 million uS dollars (uN-Comtrade, 2017). To meet the

requirements of the International plant protection Convention, South African phytosanitary policies require that all plant imports must be inspected in the country of origin, treated with pesticides and declared free of any organisms before import (Saccaggi & pieterse, 2013). despite this, organisms are often found on imported plants and plant products when inspected at South African ports of entry (Saccaggi & pieterse, 2013).

Additionally, over 20 species have been introduced as contaminants or parasites of plants, and the rate at which these organisms have been introduced has remained consistent over time (figure 3.1; also see Table A2.1). for example, Linepithema humile (Argentine ant) is believed to have been introduced to South Africa as a contaminant of imported horse fodder (picker & griffiths, 2011). Once imported, plants are intentionally transported and sold throughout the country (martin & Coetzee, 2011), and their contaminants are

potentially transported with them. The live plant trade is, therefore, an important and potentially increasing pathway through which alien organisms are introduced to the country, but this trade also likely facilitates the dispersal of alien taxa within the country after introduction.

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photographer: T. robinson

South Africa has eight major maritime ports (Richards Bay, durban, East london, Ngqura, port Elizabeth, mossel Bay, Cape Town and Saldanha Bay), and in 2016 over 8000 ocean going vessels arrived at these ports (Transnet National ports Authority, 2017). Ships can facilitate the introduction of alien taxa in a number of ways. marine organisms can be transported within the ballast water carried by ships or can attach to ships’ hulls. Through these pathways ships have facilitated the introduction of many marine taxa to South Africa (figure 3.1). In September 2017, the International maritime Organisation’s (ImO) ‘International Convention for the Control and management of Ships’ Ballast Water and Sediments’ entered into force (ImO, 2004). This convention aims to prevent the

transportation of aquatic organisms between regions, and under the convention all ships are required to manage their ballast water and sediments to a certain standard. South Africa has also drafted ballast water legislation (marine draft Ballast Water Bill), but this legislation has not yet been passed. Although there are, therefore, plans to manage the introduction of marine organisms through the release of ballast water by ships, there are currently no plans or management in place to prevent introductions through hull fouling. Over 60 alien taxa are believed to have been introduced to South Africa attached to the hulls of visiting ships, and the rate at which these

introductions have occurred has increased over time (figure 3.1; also see Table A2.1). furthermore, to deal with increasing demand, all of South Africa’s major ports, except mossel Bay, will be upgraded and expanded in the future (Transnet National ports Authority, 2014). This action could lead to an increase in the number of visiting ships, and unless additional biosecurity measures are put in place, the increased shipping intensity could result in an increase in the introduction of marine organisms through hull fouling. The threat posed by this pathway is, however, not simply in proportion to the number of visiting ships, and is higher for particular ports (durban in particular) and for particular trade routes (routes from Asia) (faulkner et al., 2017b).

the StatuS of 4

This chapter provides an overview of the status of alien species in south africa based on data from a wide range of sources (atlas projects, expert assessments, lists, and published papers and reports).

of the 2033 alien species recorded (or assumed to be present) outside of cultivation or captivity in south africa, 775 are known to be invasive, 388 are known to be naturalised but not invasive, and 355 are present, but not naturalised. for the remainder (516 species), there is insufficient information to assign them to an introduction status category. eight of the alien species recorded as present in the country are currently listed in the nem:ba regulations as prohibited (i.e. species assumed to be absent from south africa and which may not be imported).

large numbers of alien species have relatively restricted distributions. only in the case of plants and birds are there widespread species [e.g. found in at least a quarter (i.e. > 500) of the quarter-degree grid cells (Qdgcs) of south africa].

at least one alien reptile and two terrestrial invertebrate species are relatively widespread (> 100 Qdgcs), although the data coverage is poor, so there is a low level of confidence in these estimates.

The only data available to estimate the abundance of alien species are those for terrestrial and freshwater plants. These estimates are very crude or over 20 years out of date, so the level of confidence in these estimates is very low. There are no comparable data for any other high-level taxa.

a systematic evaluation of the impacts of individual invasive species as per the recently developed international standards has not yet been conducted.

however, 25 species were assessed by experts as having a severe impact, and 82 as having a major impact. of these 107 species, most (80) are terrestrial or freshwater plants, eight are mammals, five each are freshwater fish, freshwater invertebrates and terrestrial invertebrates, two are amphibians, and there is one bird and one marine plant species.

alien plants are the most diverse, widespread and damaging group of invaders in south africa. furthermore, it is clear that south africa has a major alien plant invasion debt. Well over 100 new taxa have been recorded as naturalised or escapes from cultivation over the past decade, and the recorded range of almost all plants has increased significantly. This is a significant cause for concern, as it clearly indicates that problems associated with alien species are set to increase.

Tephrocactus articulates (pine cone cactus) – sanbi

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4.1. iNtroduCtioN

This chapter provides an overview of the numbers, extent, abundance and impact of alien species in south africa. The number of species was estimated using the list in the nem:ba a&is regulations as a starting point, and adding other (unlisted) species that have been reported as naturalised in south africa.

The relevant indicators are the Number and status of alien species (i.e. whether they are known to be present in south africa and their stage of introduction); the Extent of alien species (at national, provincial, biome or other scales); the Abundance of alien species status (in terms of their cover, biomass or population sizes); and the Impact of alien species (the degree to which the species has negative impacts).

see Table 2.3 for further details.

data were obtained from a variety of sources (Table 4.1). These data were of varying quality, and this affected the level of confidence placed in each indicator.

in addition, the available data covered some, but not all, of the information needed to assign values to indicators, and for some indicators it is not yet possible to assign values due to a lack of data (Table 4.2).

tABle 4.1 Sources of data used to assign values to species indicators, with levels of confidence based on the completeness and accuracy of data sets. Source Institutions for data: Animal Demography Unit (ADU); Centre for Invasion Biology (C•I•B ); KwaZulu-Natal Museum (KZN Museum); Plant Protection Research Institute of the Agricultural Research Council (ARC-PPRI); South African Institute of Aquatic Biodiversity (SAIAB); South African National Biodiversity Institute (SANBI); South African National Parks (SANParks);

Stellenbosch University (SU); University of Cape Town (UCT); University of KwaZulu-Natal (UKZN); University of Pretoria (UP). The numbering of indicators is based on chapter 2: 5. Number and status of alien species; 6. Extent of alien species; 7. Abundance of alien species; 8. Impact of alien species.

tAxon SourCe (See All cape nature Totals provided for


individual protected areas moderate to low, depending on the

(uP) 47 database of alien species

occurring on the Prince

individual protected areas moderate to low, depending on the



are terrestrial or freshwater plants


are mammals


marine invertebrate


each are freshwater fish, freshwater invertebrates

ChaPter 4IThe sTaTus of alien sP

species list 556 taxa are listed, but the number of species listed as invasive in the nem:ba a&is regulations, or prohibited species found to be present in south africa.

(2017)* 552 a simple scoring system

was used to classify the alien species according to the relative degree of their benefits and negative

49 ditsong national museum of

natural history collection

44 spatial database (frog and

reptile atlases) housed at the adu, ucT

high for amphibians moderate for reptiles

5, 6, 8

Animals Picker & griffiths

(2017)* 571 comprehensive listing of

alien animal species in south africa

low 5, 6

Birds dr rob little (adu/

ucT) 49 spatial database (bird atlas)

housed at the adu, ucT high – monitoring of distribution is

(2017a)* 274 description of how alien

species might have been

Freshwater fish marr et al. (2017)* 27 freshwater fish species introduced into the water courses of south africa

moderate 5, 8

Freshwater fish saiab few assessments of

species-specific impacts published in the scientific literature, and in theses

(de moor, 2015). 3 specimen records held in the national collection of

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invertebrates moderate – data consistently updated

status of aquatic weeds in south africa, their

invertebrates Zachariades et al.

(2017)*; Klein (2011)

95 assessment of the status of

biological control as a management tool for suppression of invasive alien plants in south africa;

and a published review of biological control agents

high 5


invertebrates iziko sa museum:

marine invertebrate back to 1871 and includes 76 184 entries

93 list provided by experts low – based only on preliminary surveys

Microbial species Wood (2017)* 112 Preliminary listing of alien

fungal species very low 5

4 distribution records for the

reptiles of southern africa,

et al. (2016) 103 recently published review

of soil biota low 5, 6

terrestrial and freshwater


bews herbarium

(uKZn) 168 database of well-identified

and fairly extensive invasive

401 bodaTsa is a database that

contains the official plant five herbaria. This is to maintain the most current

ChaPter 4IThe sTaTus of alien sP

773 atlas maintained by the

PPri-arc moderate – based on

roadside surveys of

visser et al. (2017b)* 256 review of grasses as invasive alien plants in

(gess, 2015) 72 database of the terrestrial

insect collections of the

(sanbi) 9 list provided by expert low 5


107 Prinsloo & uys (2015) provided detailed accounts of 693 insect pests of cultivated plants and pastures in south africa; of these, 107 (14.6%) were

david Kesner (su) 16 assessments of impacts as

part of an ongoing study moderate 8

terrestrial invertebrates


Prof dai herbert

(KZn museum) 39 database and specimens

curated by the KZn

garcia (2017) * 15 impacts of invasive alien plants on abundance,

(cacti) Kaplan et al. (2017)* 31 an assessment of the status of cactus invasions in south africa.

moderate 5, 6

* Papers were part of the journal special issue that was produced as part of the status report process, see box 1.3.

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tABle 4.2 estimated completeness and accuracy of data required to assign values to alien species indicators in South Africa for different taxonomic groups. The taxonomic groupings are as per the NeM:BA A&IS Regulations. levels of completeness are: High (information available for > 75% of species); Moderate (information available for 30–75% of species); low (information available for

< 30% of species). levels of accuracy refer to available data, as follows: High (point distribution data available, or ecology and impacts well-documented); Moderate (quarter-degree grid cell distribution data available or superficial studies available on ecology and impacts); low (no formal mapping or documented studies on ecology and impacts). N/A is not applicable.

indiCAtor tAxon CoMpleteneSS ACCurACy

number and status of alien species

number and status of alien species